Sex Differences Overrated?

Aug. 21, 2007 -- Many studies claim that a genetic mutation causes more
disease in one sex than in another -- but most are wrong.

This provocative statement comes from Nikolaos A. Patsopoulos, MD, of the
University of Ioannina School of Medicine, Greece, and colleagues. It's a shot
across the bow for researchers tempted to make claims their studies do not
actually support.

Patsopoulos and colleagues looked at 77 studies published in the medical
literature. All of the studies prominently claimed to have discovered that a
genetic variation is more likely to cause disease in one sex than in
another.

The 77 studies made 432 claims of sex differences. The Patsopoulos team
evaluated the statistical methods used in the studies and reanalyzed the data
using appropriate statistical techniques.

The researchers were able to
reanalyze data in 188 claims. In the end, fewer than half the claims
(44%) had even borderline statistical significance -- that is, five-in-100 odds
that the finding was chance. Only 44 of the 432 claims had "modest"
statistical significance -- one-in-100 to five-in-100 odds the finding was
chance.

Of the 60 most valid claims, only one was consistently validated in at least
two other studies.

"At a minimum, the studies that we evaluated are probably among the ones
in which authors were most certain about some, if not all, of the sex claims
that they presented in their results," Patsopoulos and colleagues note.
"Otherwise, they would not have drawn attention to the claims in the titles
of their articles."

Analyzing research findings by sex is only the most common way researchers
break down their findings. After data is collected, researchers often go back
and analyze according to age, race, diet, lifestyle, and many other patient
characteristics.

But these analyses are valid only when researchers planned for them in
advance by including enough people in each subgroup to give the study the
necessary statistical power.

"The vast majority of claimed subgroup differences are likely to be
chance findings," Patsopoulos and colleagues conclude.

Their findings appear in the Aug. 22/29 issue of The Journal of the
American Medical Association.